It is a common requirement on construction projects that organic surficial soils (i.e., "topsoil") present on the project site must be removed and stockpiled for eventual replacement after work on the site has been completed, in order to comply with land reclamation provisions contained in environmental legislation. A further common requirement is that the topsoil must be removed to fairly precise tolerances, removing substantially all of the topsoil without removing a significant amount of the clay or other non-organic subsoil underlying the topsoil. This requirement arises from environmental regulations which restrict the permissible amount of "admixing" (i.e., mixing of topsoil and subsoil), such that the material which is replaced during site reclamation will be substantially the same topsoil which was stripped from the site before the construction work began.
These legislated requirements necessitate accurate control of the depth to which the topsoil is stripped. Accurate depth control can be accomplished fairly easily using conventional earthmoving equipment such as graders and bulldozers when the soil is not frozen. The task is considerably more difficult, however, when the soil is frozen. One method which has been used to break up frozen topsoil involves the use of heavy ripping claws (or "rippers" as they are known in the prior art) mounted to the rear end of a bulldozer. The rippers may be lowered so as to engage and break up the frozen soil as they are pulled along behind the bulldozer. Each ripper typically has a hardened steel ripper tooth oriented generally downward and toward the front of the bulldozer, such that forward movement of the bulldozer tends to draw the ripper tooth down into the ground.
One practical problem with these prior art rippers is that instead of merely breaking up soil to the depth that they have been lowered into the ground, they tend to gouge out large irregular chunks of soil. Such chunks are inconvenient to handle and must be broken up into small particles before the topsoil can be rendered properly compactable and thus usable for site reclamation. As well, because conventional box beams typically can accommodate only two or three rippers, the rippers are spaced up to two feet or more apart from each other, with the result that a significant portion of the soil surface will not be directly penetrated by the ripper teeth in a given single pass by the bulldozer/ripper equipment.
Controlling the depth of soil penetration is a particular problem with conventional rippers. Due to the configuration and orientation of the ripper teeth, forward motion of the bulldozer may tend to draw the ripper teeth deeper into the ground than desired. Even if a bulldozer operator is able to control the depth of penetration of the rippers within a satisfactory tolerance, the chunks of soil removed using rippers often contain not only topsoil, but also substantial amounts of subsoil which has become bonded to the topsoil due to freezing. If such chunks of mixed topsoil and subsoil are eventually broken up, the inevitable result will be admixing, which may render the material unusable for reclamation purposes. This problem may be addressed by importing additional topsoil to replace any topsoil which was taken from the site but which was unusable due to unsuitable particle size or admixing, or both. However, this option is expensive or may be precluded where the relevant environmental legislation requires reclamation to be accomplished using materials originally present on the site, such that imported material is permitted only in small quantities, if at all.
Canadian Patent Application No. 2,237,001 (filed on Jul. 10, 1998 by Biegel et al. and laid open on Aug. 10, 1998) discloses one attempt to find a better way of stripping frozen topsoil to a desired depth. The frozen topsoil cutter taught by Biegel may be summarized as an implement which may be hitched to and pulled behind a bulldozer, with a number of cutting wheels rotating about horizontal axes perpendicular to the direction of travel. The cutting wheels are arranged in a "vee" formation, with the apex of the vee oriented toward the front of the bulldozer. As the bulldozer moves forward, the cutting wheels may penetrate into the frozen soil to a desired depth, thereby cutting and fragmenting the soil. In order for the cutting wheels to penetrate the frozen soil, they must operate under constant and substantial vertical loading. The required vertical loading may be provided by hydraulic rams associated with the bulldozer, or simply by adding removable weights to the frame of the implement.
The need for the cutting wheels to be under constant and substantial vertical loading is a significant disadvantage. If the loading is too small, the cutting wheels will not penetrate as deeply as desired, and the cutting procedure may have to be repeated in order to strip all of the topsoil. If the loading is too great, the cutting wheels may penetrate beneath the topsoil layer into the subsoil, resulting in undesirable admixing. Even when the thickness of the frozen topsoil is of a known and essentially constant thickness, in order for the Biegel implement to break up all of the topsoil, and only the topsoil, the downward force acting on the cutting wheels may require constant adjustment in response to variations in the soil's resistance to penetration. In any event, use of the Biegel device requires constant vigilance on the part of the operator to ensure that the desired results are being accomplished.
Considering all the foregoing factors, there is clearly a need in the art for a frozen topsoil plowing implement which can cut and loosen frozen topsoil to a desired depth below the ground surface, without also loosening soil from below the desired depth, and without loosening the topsoil in fragments of such dimensions that they would require further fragmentation or pulverizing in order to be suitable for land reclamation purposes. There is furthermore a need for a frozen topsoil plowing implement which does not require, for its effective functioning, the provision of vertical loads acting on the implement over and above the vertical loads inherently provided by the dead weight of the implement's structure.